A conventional publish/subscribe messaging architecture includes publishers and subscribers. In such a messaging architecture, the publishers do not have any specific subscriber knowledge and thus do not send messages directly to the subscribers. Rather, the publishers publish messages to intermediaries, and the subscribers await receipt of (or listen for) the published messages from the intermediaries.
In a conventional publish/subscribe messaging architecture that is topic-based, a publisher publishes (or posts) messages to a topic. Here, the subscribers that subscribe to that topic receive the messages that are posted to that topic.